cpp/third_party/antlr4-cpp-runtime-4/runtime/src/dfa/DFAState.h

/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

#pragma once

#include "antlr4-common.h"

namespace antlr4 {
namespace dfa {

  /// <summary>
  /// A DFA state represents a set of possible ATN configurations.
  ///  As Aho, Sethi, Ullman p. 117 says "The DFA uses its state
  ///  to keep track of all possible states the ATN can be in after
  ///  reading each input symbol.  That is to say, after reading
  ///  input a1a2..an, the DFA is in a state that represents the
  ///  subset T of the states of the ATN that are reachable from the
  ///  ATN's start state along some path labeled a1a2..an."
  ///  In conventional NFA->DFA conversion, therefore, the subset T
  ///  would be a bitset representing the set of states the
  ///  ATN could be in.  We need to track the alt predicted by each
  ///  state as well, however.  More importantly, we need to maintain
  ///  a stack of states, tracking the closure operations as they
  ///  jump from rule to rule, emulating rule invocations (method calls).
  ///  I have to add a stack to simulate the proper lookahead sequences for
  ///  the underlying LL grammar from which the ATN was derived.
  /// <p/>
  ///  I use a set of ATNConfig objects not simple states.  An ATNConfig
  ///  is both a state (ala normal conversion) and a RuleContext describing
  ///  the chain of rules (if any) followed to arrive at that state.
  /// <p/>
  ///  A DFA state may have multiple references to a particular state,
  ///  but with different ATN contexts (with same or different alts)
  ///  meaning that state was reached via a different set of rule invocations.
  /// </summary>
  class ANTLR4CPP_PUBLIC DFAState {
  public:
    class PredPrediction {
    public:
      Ref<atn::SemanticContext> pred; // never null; at least SemanticContext.NONE
      int alt;

      PredPrediction(const Ref<atn::SemanticContext> &pred, int alt);
      virtual ~PredPrediction();

      virtual std::string toString();

    private:
      void InitializeInstanceFields();
    };

    int stateNumber;

    std::unique_ptr<atn::ATNConfigSet> configs;

    /// {@code edges[symbol]} points to target of symbol. Shift up by 1 so (-1)
    ///  <seealso cref="Token#EOF"/> maps to {@code edges[0]}.
    // ml: this is a sparse list, so we use a map instead of a vector.
    //     Watch out: we no longer have the -1 offset, as it isn't needed anymore.
    std::unordered_map<size_t, DFAState *> edges;

    bool isAcceptState;

    /// if accept state, what ttype do we match or alt do we predict?
    /// This is set to <seealso cref="ATN#INVALID_ALT_NUMBER"/> when <seealso cref="#predicates"/>{@code !=null} or
    /// <seealso cref="#requiresFullContext"/>.
    size_t prediction;

    Ref<atn::LexerActionExecutor> lexerActionExecutor;

    /// <summary>
    /// Indicates that this state was created during SLL prediction that
    /// discovered a conflict between the configurations in the state. Future
    /// <seealso cref="ParserATNSimulator#execATN"/> invocations immediately jumped doing
    /// full context prediction if this field is true.
    /// </summary>
    bool requiresFullContext;

    /// <summary>
    /// During SLL parsing, this is a list of predicates associated with the
    ///  ATN configurations of the DFA state. When we have predicates,
    ///  <seealso cref="#requiresFullContext"/> is {@code false} since full context prediction evaluates predicates
    ///  on-the-fly. If this is not null, then <seealso cref="#prediction"/> is
    ///  <seealso cref="ATN#INVALID_ALT_NUMBER"/>.
    /// <p/>
    ///  We only use these for non-<seealso cref="#requiresFullContext"/> but conflicting states. That
    ///  means we know from the context (it's $ or we don't dip into outer
    ///  context) that it's an ambiguity not a conflict.
    /// <p/>
    ///  This list is computed by <seealso cref="ParserATNSimulator#predicateDFAState"/>.
    /// </summary>
    std::vector<PredPrediction *> predicates;

    /// Map a predicate to a predicted alternative.
    DFAState();
    DFAState(int state);
    DFAState(std::unique_ptr<atn::ATNConfigSet> configs);
    virtual ~DFAState();

    /// <summary>
    /// Get the set of all alts mentioned by all ATN configurations in this
    ///  DFA state.
    /// </summary>
    virtual std::set<size_t> getAltSet();

    virtual size_t hashCode() const;

    /// Two DFAState instances are equal if their ATN configuration sets
    /// are the same. This method is used to see if a state already exists.
    ///
    /// Because the number of alternatives and number of ATN configurations are
    /// finite, there is a finite number of DFA states that can be processed.
    /// This is necessary to show that the algorithm terminates.
    ///
    /// Cannot test the DFA state numbers here because in
    /// ParserATNSimulator#addDFAState we need to know if any other state
    /// exists that has this exact set of ATN configurations. The
    /// stateNumber is irrelevant.
    bool operator == (const DFAState &o) const;

    virtual std::string toString();

    struct Hasher
    {
      size_t operator()(DFAState *k) const {
        return k->hashCode();
      }
    };

    struct Comparer {
      bool operator()(DFAState *lhs, DFAState *rhs) const
      {
        return *lhs == *rhs;
      }
    };

  private:
    void InitializeInstanceFields();
  };

} // namespace atn
} // namespace antlr4